Introduction

Power generated in power stations pass through large and complex networks like transformers, overhead lines, cables and other equipment and reaches at the end users.

Total Losses in Power Distribution and Transmission Lines (photo credit: Total Losses in Power Distribution and Transmission Lines (on photo: A transmission line of constant voltage of 600 kVDC, at 2400 kilometers built in Brazil; credit: IVOLINES via Flickr)

It is fact that the unit of electric energy generated by Power Station does not match with the units distributed to the consumers. Some percentage of the units is lost in the distribution network.

This difference in the generated and distributed units is known as Transmission and Distribution loss. Transmission and Distribution loss are the amounts that are not paid for by users.

Distribution Sector considered as the weakest link in the entire power sector. Transmission Losses is approximate 17% while Distribution Losses is approximate 50%.

There are two types of Transmission and Distribution Losses:

Technical Losses

Non Technical Losses (Commercial Losses)

1. Technical Losses

The technical losses are due to energy dissipated in the conductors, equipment used for transmission line, transformer, subtransmission line and distribution line and magnetic losses in transformers.

Technical losses are normally 22.5%, and directly depend on the network characteristics and the mode of operation.

The major amount of losses in a power system is in primary and secondary distribution lines. While transmission and sub-transmission lines account for only about 30% of the total losses. Therefore the primary and secondary distribution systems must be properly planned to ensure within limits.

The unexpected load increase was reflected in the increase of technical losses above the normal level

Losses are inherent to the distribution of electricity and cannot be eliminated.

There are two Type of Technical Losses.

1. Permanent / Fixed Technical losses

Fixed losses do not vary according to current. These losses take the form of heat and noise and occur as long as a transformer is energized

Between 1/4 and 1/3 of technical losses on distribution networks are fixed losses. Fixed losses on a network can be influenced in the ways set out below

2. Variable Technical losses

Variable losses vary with the amount of electricity distributed and are, more precisely, proportional to the square of the current. Consequently, a 1% increase in current leads to an increase in losses of more than 1%.

Between 2/3 and 3/4 of technical (or physical) losses on distribution networks are variable Losses.

By increasing the cross sectional area of lines and cables for a given load, losses will fall. This leads to a direct trade-off between cost of losses and cost of capital expenditure. It has been suggested that optimal average utilization rate on a distribution network that considers the cost of losses in its design could be as low as 30 per cent.

Main Reasons for Technical Losses

1. Lengthy Distribution lines

In practically 11 KV and 415 volts lines, in rural areas are extended over long distances to feed loads scattered over large areas. Thus the primary and secondary distributions lines in rural areas are largely radial laid usually extend over long distances.

This results in high line resistance and therefore high I2R losses in the line.

Haphazard growths of sub-transmission and distribution system in to new areas.

Large scale rural electrification through long 11kV and LT lines.

2. Inadequate Size of Conductors of Distribution lines

The size of the conductors should be selected on the basis of KVA x KM capacity of standard conductor for a required voltage regulation, but rural loads are usually scattered and generally fed by radial feeders. The conductor size of these feeders should be adequate.

3. Installation of Distribution transformers away from load centers

In most of case Distribution Transformers are not located centrally with respect to consumers. Consequently, the farthest consumers obtain an extremity low voltage even though a good voltage levels maintained at the transformers secondary.

This again leads to higher line losses. (The reason for the line losses increasing as a result of decreased voltage at the consumers end therefore in order to reduce the voltage drop in the line to the farthest consumers, the distribution transformer should be located at the load center to keep voltage drop within permissible limits.)

4. Low Power Factor of Primary and secondary distribution system

In most LT distribution circuits normally the Power Factor ranges from 0.65 to 0.75. A low Power Factor contributes towards high distribution losses.

For a given load, if the Power Factor is low, the current drawn in high And the losses proportional to square of the current will be more. Thus, line losses owing to the poor PF can be reduced by improving the Power Factor.

This can be done by application of shunt capacitors.

Shunt capacitors can be connected either in secondary side (11 KV side) of the 33/11 KV power transformers or at various point of Distribution Line.

The optimum rating of capacitor banks for a distribution system is 2/3rd of the average KVAR requirement of that distribution system.

The vantage point is at 2/3rd the length of the main distributor from the transformer.

A more appropriate manner of improving this PF of the distribution system and thereby reduce the line losses is to connect capacitors across the terminals of the consumers having inductive loads.

By connecting the capacitors across individual loads, the line loss is reduced from 4 to 9% depending upon the extent of PF improvement.

Feeder phase unbalance may vary during the day and with different seasons. Feeders are usually considered “balanced” when phase current magnitudes are within 10.Similarly, balancing load among distribution feeders will also lower losses assuming similar conductor resistance. This may require installing additional switches between feeders to allow for appropriate load transfer.

Bifurcation of feeders according to Voltage regulation and Load.

7. Load Factor Effect on Losses

Power consumption of customer varies throughout the day and over seasons.

Residential customers generally draw their highest power demand in the evening hours. Same commercial customer load generally peak in the early afternoon. Because current level (hence, load) is the primary driver in distribution power losses, keeping power consumption more level throughout the day will lower peak power loss and overall energy losses.

Load variation is Called load factor and It varies from 0 to 1.

Load Factor = Average load in a specified time period / peak load during that time period.

For example, for 30 days month (720 hours) peak Load of the feeder is 10 MW. If the feeder supplied a total energy of 5,000 MWH, the load factor for that month is (5,000 MWh)/ (10MW x 720) =0.69.

Lower power and energy losses are reduced by raising the load factor, which, evens out feeder demand variation throughout the feeder.

The load factor has been increase by offering customers “time-of-use” rates. Companies use pricing power to influence consumers to shift electric-intensive activities during off-peak times (such as, electric water and space heating, air conditioning, irrigating, and pool filter pumping).

With financial incentives, some electric customers are also allowing utilities to interrupt large electric loads remotely through radio frequency or power line carrier during periods of peak use. Utilities can try to design in higher load factors by running the same feeders through residential and commercial areas.

8. Transformer Sizing and Selection

Distribution transformers use copper conductor windings to induce a magnetic field into a grain-oriented silicon steel core. Therefore, transformers have both load losses and no-load core losses.

Transformer copper losses vary with load based on the resistive power loss equation (P loss = I2R). For some utilities, economic transformer loading means loading distribution transformers to capacity-or slightly above capacity for a short time-in an effort to minimize capital costs and still maintain long transformer life.

However, since peak generation is usually the most expensive, total cost of ownership (TCO) studies should take into account the cost of peak transformer losses. Increasing distribution transformer capacity during peak by one size will often result in lower total peak power dissipation-more so if it is overloaded.

9. Balancing 3 phase loads

Balancing 3-phase loads periodically throughout a network can reduce losses significantly. It can be done relatively easily on overhead networks and consequently offers considerable scope for cost effective loss reduction, given suitable incentives.

10. Switching off transformers

One method of reducing fixed losses is to switch off transformers in periods of low demand. If two transformers of a certain size are required at a substation during peak periods, only one might be required during times of low demand so that the other transformer might be switched off in order to reduce fixed losses.

This will produce some offsetting increase in variable losses and might affect security and quality of supply as well as the operational condition of the transformer itself. However, these trade-offs will not be explored and optimized unless the cost of losses are taken into account.

11. Other Reasons for Technical Losses

Unequal load distribution among three phases in L.T system causing high neutral currents.

leaking and loss of power

Over loading of lines.

Abnormal operating conditions at which power and distribution transformers are operated

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Jignesh Parmar has completed M.Tech (Power System Control), B.E (Electrical). He is member of Institution of Engineers (MIE), India. He has more than 13 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.

50 Comments

Sakhare Chandrakant

Nov 16, 2018

Sir, how calculate station loss, Transformer loss
We have 2nos of 220kv I/C line and 8nos of 110kv O/G feeder, in day time solar injection from 7nos 110kv line is high that power stepup and given 220 kv grid, in night time it just opposite power drawn from grid consuming 8nos of feeders, here we can export and import energy for individual feeder but how to calculate for entire Receiving Station

The same article is available in ELECTRICAL INDIA Vol 58 Jan 2018 As a front page article details at Page No 38.

Further step of your line losses, please take a study/ already done please share….

We need to highlight 11 Kv effects on single phase line at jumping, as long running as kms in rural areas both lines together in same poles with non maintained distance.
Many times due to birds lands, wind, tree branches touching the both lines same times, Vehicle accidents to poles, other uncontrolled effects fraction of seconds to some seconds both the HT and LT powers linked each other cause heavy damage in single phase connected loads.

TC centers also not maintained in all rural areas of the country cause the major burns of house hold single phase load including public street light mainly during rainy season starts.as observed…

Dear Sir
I want calculate the power loss in distribution cable by inductive load.The formula of line power loss is P=RI^2 for each phase.so if it is true how can i calculate the I parameter in lag load.
thanks

sir, In our company their were 3 divisions each division has a check meter for individual kwh consumption,as a basis for our individual payment of our bills and a primary meter to sum total consumption for the 3 divisions.1.) their is a current loss or difference between the primary meter reading and the total check meter reading after we add all the meter readings of the 3 division check meter. Example: Total kwh used by Divisions: a. 22,000kwh b. 12,000kwh c. 10,000kwh = 44,000kwh, and the primary meter is=39,000kwh or a 5,000kwh difference. HOw can we distribute the 5,000kwh difference for the 3 divisions? can you give us a mathematical furmula/computation, so that we can fairly distribute this to users?
Thank you;
JUn

1. When you say “Distribution Sector considered as the weakest link in the entire power sector. Transmission Losses is approximate 17% while Distribution Losses is approximate 50%.”, you’re referring to 17% of what and 50% of what?

2. When you say “Technical losses are normally 22.5%”, do you mean technical losses are 22.5% of the total T&D losses?

DEAR Sir
Thank you for your published
I have one question about the references of your paper. For example in the first part of your paper you aimed that technical loss is normally near 22%. would you please tell me abut the references of that?
with best regard
Kazem

Please i intend to do a design for power plant using gas engines (about 5MW capacity) to export power to a customer on overhead lines of about 6KM, please how do i calculate the line power loss if customer requires on about 4MW of power.

Hello. I was under the understanding that the reason for raising the voltage of electricity prior to transmission was to reduce the loss occurring between source and load by relying on the fact that the power dissipated is (V^2)/R so that current “I” would be low thus (I^2)R would be low even for high “R” and that for high “R” (V^2)/R would be low. In this article it is written that cables and other transmission conductors are made with higher cross section in order to lower resistance and thus lower (I^2)R. From what I gather having read this article, this applies mainly to the higher current more local distribution systems closer to the consumer. Please correct me if I am mistaken as I am not a power distribution engineer.

sir, i am working in a power distribution company and i found that when the 33/11 kv power transformer was on no load and was only feeding from 132 kv ss to its 33 kv side it was taking 2.2 A to 2.7 A on 33 kv side also it includes the subtransmission loss from 132 / 33 kv sub station, then i calcute its energy consumed or loss for 1 hour as :
1.732 * 33000 (V) * 2.2 (A) * 1 (hour) = 125743.2 WH = 125.743 KWH
So does it mean the 125.743 kwh are the loss ?
Please analyse my analysis ..

Thank You for sharing the article. Transmission and Distribution Losses are great threat for energy solutions. Big Hybrid generators with low budget are a great solution for energy and power. Really an informative thread.

Sir…. NJY feeder (Which are feeding power supply to rural area villages) are having 40% loss ,these feeders are running 30Kms HT LINE and 60Kms LT LINE reasons for such a huge losses..Peak load of these feeders are 30Amps…HT Conductor is rabit and LT Conductor is weasel…

Sir, Very good article explaining distribution loss and ways to correct it. I help industrial companies reduce distribution losses typically by installing shunt capacitors at the load. Often these induction motors can be from 30-150 hp and located over 100 ft from the transformer. how do you recommend calculating the distribution loss and the savings based on capacitor installation? You mentioned a range from 4-9%. Thank you. Kent

I find your article useful. I am a student working on Simulation and Analysis of Technical Losses on Electric power Transmission Line. Can you please provide me materials on Technical Losses on Transmission Lines for my study?

System or technical losses can be estimated by modelling the system. These can be checked against substation feeder measurements. When these losses appear to be excessive, check for “non-technical” losses. I encountered a situation some years ago in which the meter for one of the largest loads in a small community was not wired correctly, with the result that the measured energy use of the cusomer was a tiny fraction of actual use. Re-wiring that meter dropped system losses in half, and considerably improved the balance sheet of the small utility involved. It is unknown whether intentional theft was involved. Of course, meters must be locked securely. Modern data processing methods can be used to identify customer services with suspiciously low energy use.

The technical losses quoted in this article seem rather high by North American standards. I recollect that EIA data suggests more like 3% of losses in the transmission system and 5% in the distribution system. Was the 22.5% technical loss figure specifically for, eg, India.

It depends on calculation….in india i have generated thounsand of feeders in Cymdist..(cyme cooper power) application but while calculating the instantaneous tech loss report…%loss was ranging from 5 to 25% or more…but the same feeder if calculate with monthly load survey data it was below 5%.

I have built a 50 KW Microhydel Power project. The Total No of house holds is 106. These house holds are to be electrified from the project. I want to transmit the voltage by stepping it up to 415/11000 Volts through step up transformer of 62.5 KVA. There are two other step down Distribution transformers of 25 KVA. I want to transmit the step up voltage by using GNAT ACSR over head conductor of 25 mm^2 an and want to use Rabbit AC of 50mm^2. Now i want to calculate The entire area of transmission net work is nearly 5 KM and distribution area is about 13 Km. I want to calculate the transmission and distribution line losses. Plz help me thanks

ACSR Stands for Alluminium conductors Steel Reinforced. GNAT(GEENAT) is used for Commercial Name of the overhead Conductors.
Sorry it is not Rabbit AC it is Rabbit AAC(All alluminium Conductors)
Pleas please help me to calculate losses in transmission and distribution lines

I have built a 50 KW Microhydel Power project for the community of a small village.The Total No of house holds is 106. These house holds are to be electrified from the project. I want to transmit the voltage by stepping it up to 415/11000 Volts through step up transformer of 62.5 KVA. There are two other step down Distribution transformers of 25 KVA. Total Distance for Transmission line is 4 Kilometer and for Distribution line, it is 12 Kilomenter.
Plz help me in calculating of

1- Size of Overhead conductor for Transmission and Distribution Line
2- Losses in Transmission line
3- Losses in Distribution line
I shall be very thankful if some friends may help me
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